The present patent application relates to lawn and garden equipment, and, more particularly, to a rotary tiller having a transmission and drive system at least partially disposed within a cylindrical drum.
Several types of rotary tillers exist for performing various tilling operations in gardens, flowerbeds, lawns, or the like. Examples of these types include rear tine SRT (“standard rotating tine”) tillers, rear tine CRT (“counter rotating tine”) tillers, and front tine tillers, also commonly referred to as cultivators. While each of these devices is capable of tilling the earth, each particular construction can be optimized for discrete operating conditions or operations.
Rotary tillers generally include a series of tines which are mounted on a single horizontal tiller shaft and rotated in order to provide a slicing action in which the tines cut through the soil. Many rotary tillers provide power and rotation to the tiller shaft through a worm drive. In worm drive systems, a motor drive shaft includes a worm portion that is configured to engage a worm gear extending around and coupled to the tiller shaft. In operation, rotation of the motor drive shaft is transferred to the tiller shaft through the interaction of the worm and the worm gear. Worm gear drives are popular because they allow for a significant reduction in rotational speed, while also allowing a higher torque to be transmitted to the tiller shaft.
Conventional, high-reduction worm drive rotary tillers are inefficient. In the past, efficiency of the worm drive gearbox was not a concern because rotary tillers are typically heavy pieces of gas powered equipment with a replenishipable fuel source. However, if a compact, lightweight tiller is desired that operates on a limited power supply, such as a battery, the run time of the rotary tiller can be severely inhibited by the inefficiency of the gearbox.
Current rotary tillers that incorporate a worm drive reduction on the tine shaft leave an untilled strip in the center of the tilling path because the worm shaft that transmits power to the worm gear on the tine shaft cannot interfere with the tines as they rotate. Therefore, the depth of the cut made by the tines is limited by the existence of the uncut strip of soil coming into contact with the transmission housing. Rotary tillers that incorporate a chain drive reduction rather than a worm drive reduction on the tine shaft also leave an untilled strip in the center of the tilling path for similar reasons. Alternatively, chain drive reductions can be located on either end of the tine shaft. However, when this style of reduction is used, the tine hood and the chain reduction create obstacles that also limit the depth of the cut.
As discussed above, many tiller worm drives utilize large gear reductions with small diameter tine shafts to reduce rotational speed and increase torque. However, several problems relating to vegetation can occur with such a configuration. For example, vegetation commonly wraps around the small tine shaft very tightly because the small tine shaft has a large mechanical advantage. Additionally, the portion of the motor drive shaft that is exposed to the vegetation creates a location for the stationary surfaces of the rotary tiller to hold the vegetation while the rotating tines and tine shaft tightly wind the vegetation. This condition is generally compounded by the presence of bolts protruding from both the transmission and the tine shaft, as well as the presence of tines on either side of the transmission that grab the same vegetation and bend it around both sides of the transmission simultaneously. Additionally, when dealing with high reduction worm drives, the tine shaft is difficult to move by human power when the rotary tiller is powered down. In this case, the tines may need to be removed prior to unwinding the vegetation.